This is Oregon's Columbia county which is the next county east from Clatsop where Astoria is located.  The town of Mist is just off the bottom of the image where the 202 and the 47 intersect.  The 202 starts in Astoria and wanders southeast through Clatsop county, intersecting highway 103  and then starts wandering east to Mist and onward to cross the Columbia R at Longview ,WA.  The river that runs alongside the 202 in the SW corner of the image is the Nehalem R which crosses under the 202's bridge near the western edge of the map.

Finally, I wound up talking to a couple of folks I know who used to work at the NASA facility in Slidell, LA.  One of them told me that the black rectangles (for the most part) were added to images in the early 2000s as a means to provide some protection for infrastructure sites like power company/coop switching yards and trainyards.

Mark Bozanich at the WSDOT, who says he's been a map geek since he was 5, solved the mystery.  Unfortunately, I didn't start spending my summer vacations with my folks' collection of NGS maps until I was 7.  And, I've sent him a thank you.

virginia